A neuronal projection has been neuroanatomically identified to originate from the midbrain raphe nuclei and to terminate in the hypothalamic suprachiasmatic nuclei. These neurons have been further identified neuro- chemically to contain serotonin and to release this monoamine at their suprachiasmatic terminals. A body of evidence suggests that these raphe- suprachiasmatic serotoninergic neurons and neurons in the supra-chiasmatic nuclei which contain LH-releasing factor (LH-RF) are functionally linked. The serotoninergic neurons apparently exert an inhibitory control over luteinizing hormone (LH) release and ovulation. The overall objective of the proposed research research is to determine whether the raphe-suprachiasmatic serotoninergic neurons and the suprachiasmatic median eminence LH-RF neurons represent a neuronal- neurosecretory system which functions as an integral unit. In our present studies, we are altering activity in the serotoninergic neurons using stereotaxically placed electrical and pharmacological manipulations while monitoring responses in the LH release mechanism and ovulation.